Recently, the Federal Communication Commission approved use of the 77 gigahertz (GHz) radio band for the automobile radar market. To operate at this ultra high frequency band, a transistor must have a peak transit frequency, fT, of approximately 200 GHz and a maximum oscillation frequency, fMAX, of greater than 200 GHz.
Currently, the majority of silicon-based products operating in the high frequency bands use SiGe BiCMOS (silicon germanium bipolar complimentary metal oxide semiconductor) technologies. For many of these products, a peak fMAX of 100 GHz is sufficient. In contrast, products operating at 77 GHz or another ultra high frequency band will most likely require use of a BiCMOS (bipolar complimentary metal oxide semiconductor) technology that includes a much higher performance SiGe HBT (silicon germanium heterojunction bipolar transistor) device.
Furthermore, conventional doping of the base electrode layer in a selective epitaxial base bipolar transistor occurs early in the HBT (heterojunction bipolar transistor) manufacturing process, usually during the deposition of the emitter/base stack. Following the doping, the base electrode layer is exposed to numerous low and medium temperature processes, that can induce dopant loss, cause segregation of the dopant in the oxide layers, and deactivate the dopant.
Accordingly, a need exists for a manufacturing process for a HBT that can be used at the 77 GHz radio band and increase dopant in the base electrode layer.
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The terms “first,” “second,” “third,” “fourth,” and the like in the description and in the claims, if any, are used for distinguishing between similar elements and not necessarily for describing a particular sequential or chronological order. It is to be understood that the terms so used are interchangeable under appropriate circumstances such that the embodiments of the invention described herein are, for example, capable of operation in sequences other than those illustrated or otherwise described herein. Furthermore, the terms “comprise,” “include,” “have,” and any variations thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements is not necessarily limited to those elements, but may include other elements not expressly listed or inherent to such process, method, article, or apparatus.
The terms “left,” “right,” “front,” “back,” “top,” “bottom,” “over,” “under,” and the like in the description and in the claims, if any, are used for descriptive purposes and not necessarily for describing permanent relative positions. It is to be understood that the terms so used are interchangeable under appropriate circumstances such that the embodiments of the invention described herein are, for example, capable of operation in other orientations than those illustrated or otherwise described herein. The term “coupled,” as used herein, is defined as directly or indirectly coupled in an electrical or non-electrical manner.